H. Ratajczak

New hydrogen-bonded molecular crystals with nonlinear second-order optical properties

Abstract Fifteen new hydrogen-bonded crystals exhibiting nonlinear optical properties were obtained. For the morpholinium dihydrogenphosphate crystal, the structure was determined by the X-ray diffraction methods. This crystal belongs to the P 2 1 space group of the monoclinic system. The lattice parameters are as follows: a =8.345(2), b =6.156(1), c=9.109(2) A ; β =116.64(3)°. The crystal is built up of the layers parallel to the (001) crystallographic planes. The layer consists of the dihydrogenphosphate chains running parallel to the [010] direction. The morpholinium cation participates in two hydrogen bonds with the O(4) oxygen atoms of dihydrogenphosphate anions belonging to two neighbour chains shifted by the a distance. In such a way, the chains of dihydrogenphosphates are joined by the morpholinium cations into the layer parallel to the (001) crystallographic plane. Additionally, the powder IR and Raman spectra are presented for this crystal.

Relation between O—H stretching frequency and hydrogen bond energy: re-examination of the Badger–Bauer rule

Experimentally a large number of linear relations have been found between the change in OH stretching frequency, Δ, on hydrogen bonding and the hydrogen bond energy, ΔH. A least square treatment of these Δ against ΔH relations is carried out for constant acceptor, variable donor as well as constant donor, variable acceptor systems. Generally, the constant-acceptor plots have much higher values of intercepts than the constant-donor plots. The slopes of the constant-donor plots seem to vary with the basicity of the donor . However, since Δ should go to zero when there is no interaction, it is suggested that the complete Δ against ΔH, relation could be nonlinear. Molecular orbital calculations have been employed to throw light on the Δ against ΔH relation. It is also shown that charge transfer theory when applied to the hydrogen bond predicts a relation between shown that charge transfer theory when applied to the hydrogen bond predicts a relation between ΔH and the quantity (20–2)½ where 0 and , are the free and perturbed OH stretching frequencies.

Structure and polarized IR spectra of the K2HPO4·3H2O crystal

Abstract Dipotassium hydrogenphosphate trihydrate (K 2 HPO 4 ·3H 2 O), when recrystallized from water at room temperature, is orthorhombic, space group Pbca , with a =13.813(6), b =13.808(6), c =7.775(4) A, and Z =8. The crystal structure was determined from three-dimensional X-ray diffraction data taken on an automatic diffractometer with Mo K α , and refined by least-squares techniques to R =0.034 for 1816 reflections. The HPO 2− 4 ions are joined by hydrogen bonds, with an O⋯O distance of 2.578(3) A, into chains parallel to the c axis. The chains are held together by a three-dimensional network of hydrogen bonds formed by the water molecules. The polarized absorption IR spectra at 290 K have been measured and discussed in relation to the crystal structure. The polarization features of the bands arising from the internal stretching vibrations of the HPO 2− 4 ions are predicted assuming the HOPO 2− 3 model. A strong intra-chain coupling is observed for the ν s PO 3 (40 cm −1 ) whereas a weak Davydov-type splitting (10 cm −1 ) appears for the other vibrations. The bending γOH and δOH modes of the hydrogen bonds of the chains appear at 800 cm −1 and 1220 cm −1 , respectively. The νOH absorption exhibits the ABC structure. The strong bands at 765 cm −1 , 625 cm −1 and 607 cm −1 are assigned to the twisting-type librational motions of the water molecules.

Studies on the lithium bond

Abstract Semi-empirical and ab initio calculations on 1:1 NH3lithium halide complexes show that the lithium bond is stronger than the hydrogen bonds formed by the corresponding hydrogen halides. There is an elongation of the Li-halogen bond and a decrease in the stretching force constant in the complex. Unlike in hydrogen bonds, there is an increase in charge on the bridging atom in lithium bonds.

Theoretical studies of lithium bonding in lithium chloride/aliphatic amine complexes

In the systematic study of amine … LiCl [amines = NH3, CH3NH2, (CH3)2NH] complexes the possibility of an ion-pair structure and the effect of methylation on the stabilization energy is investigated. ΔEis evaluated by the SCF/4-31G method and augmented by the approximate dispersion energy calculated perturbationally. The interaction energy decreases with the increasing number of methyl groups in the amine. The dispersion energy plays a negligible role in the stabilization of complexes. None of the systems studied are ion pairs; their Li bonds are of a so-called molecular type. Due to the divergence of the multipole expansion, the attempt to correct the 4-31G stabilization energies via the electrostatic energy fails. The relative order of the ΔE in the series of complexes is verified instead in the extended basis set calculation. The lithium bonds are compared with their H-bonded analogues.

A variable low-temperature FT-IR study of crystalline β-d-fructopyranose and deuterated analogues

Abstract FT-IR spectra have been recorded of β- d -fructopyranose and deuterated analogues at variable temperatures in the range between ambient and 100 K. The natural resolution enhancement showing up in the OH stretching region provides detailed information with respect to the system of H-bonds in the crystalline phase. Other spectral changes resulting from cooling have been studied in addition. The shift of the band maxima proves to be correlated with the H-bond geometry, i.e. the temperature sensitivity depends on the type(s) of H-bonding. The presence of vibrational coupling between some of the H-bonded OH groups has been demonstrated with deuterium exchange experiments. The peaks in the OH stretching region have been tentatively assigned based on the spectral information of the uncoupled vibrations at 100 K.

Infrared dispersion studies: 11. Band intensities and vibrational polarizations of chloroform, bromoform and their deuterated analogues

Abstract Refractive index data have been obtained between 5000 and 20 cm −1 for chloroform, bromoform and their deuterated derivatives. These dispersion data have been analyzed to yield infrared band intensities and atomic polarizations.

Properties of strong hydrogen-bonded systems: The formation of hydrogen-bonded ion pair in amine·HCL systems

Abstract The hydrogen-bonded complexes between CH 3 NH 2 and (CH 3 ) 2 NH with HCl have been studied by the ab initio molecular orbital method using the 4–31G basis set. Calculations show that the proton potential curve has a single minimum near to the nitrogen atom in both complexes. This means that the proton has been transferred from HCl to the amine. Δ E and the dipole moment of the complexes studied are as follows: −18.2 kcal mol −1 , 10.3 D for methylamine ·HCl, and −21.7 kcal mol −1 11.1 D for the corresponding dimethylamine complex. Other properties of the hydrogen-bonded ion pairs are discussed.

Far-IR spectroscopic investigations of nematic liquid crystals with hydrogen-bonded molecules

Abstract Far-IR spectroscopy (200−30 cm−1 was used to study the temperature evolution of the hydrogen bonds in the nematic liquid crystal phase of 4, n-heptyl-, octyl- and nonyl-oxybenzoic acids (HOBA, OOBA and NOBA). The observed absorption bands (νOH = 82, 68, 63 and 42 cm−1) are assigned to the four predominant vibrations respectively — stretching, bending (out of and in the dimer ring plane) and twisting. From a spectral band half-width temperature analysis hydrogen-bond evolution in the isotropic and nematic phases is investigated. A cyclic ⇌ open dimer transformation at different vibrational frequencies and polarizations is indicated.

CNDO/2 molecular orbital calculations on the complexes formed between methyllithium and trimethylaluminium with aliphatic amines

Summary A systematic CNDO/2 study has been carried out on the lithium-bonded model systems, CH 3 Li NR 3 , formed between methyllithium and aliphatic amines. The molecular complexes of trimethylaluminium with aliphatic amines have also been studied. Significant correlations between calculated molecular properties of the complexes and the ionization potentials of the amines have been found, and these are discussed on the basis of Mullikens charge transfer theory. Similarities and differences between the lithium bond and the hydrogen bond are discussed.